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Volume 15 (1981)
- Issue 6 Pages 295-
- Issue 5 Pages 229-
- Issue 4 Pages 163-
- Issue 3 Pages 109-
- Issue 2 Pages 51-
- Issue 1 Pages 1-
Volume 15, Issue 4
Displaying 1-7 of 7 articles from this issue
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Masatake Honda1981 Volume 15 Issue 4 Pages 163-181
Published: August 20, 1981
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSBy some mechanisms which have not been well explored yet, antarctic meteorites have naturally been concentrated in bare ice areas of Antarctica, and the quantities as well as the number of species of the fragments of the stone meteorites are impressively large. Based on the studies of cosmogenic nuclides in these samples, we may extend our discussions to the following problems: (1) The terrestrial ages are distributed thus far between 104 and 7·105y, or 2·105y on the average. The age seems to correspond to the mean life of the meteorites in Antarctica. (2) Their occurrences are indicating already that as a part of showers, each group of 10 to more than 100 small fragments which were recovered in small areas could be attributed to the same fall. In general, a pairing of fragments could be confirmed by the classification, the terrestrial age, the exposure age (21Ne and 40K contents), the contents of radiogenic and trapped components, etc. . On the other hand, many unpaired independent fragments have also been identified by the same measurements. (3) Although independent small meteorite falls may also be found, the majority seem to-be composed of fragments of ordinary size, 10-104 kg stone meteorites, as indicated by the 53Mn contents and the 22Ne/21Ne ratios. On the whole, local falls on the ablation area may be responsible for more than half of the total weight (depending on a material balance of ice). This amount is in the range of estimates from the world annual meteorite falls and the terrestrial age. The rest seems to be composed of many independent fragments which have been transported to the same ablation area by a local glacier. The fragments of many falls in a wide region of the accumulation area have been mixed together; and only a small fraction (10-2) has been exposed on the blue ice fields, giving an outstandingly enriched variety of meteorite species.View full abstractDownload PDF (5962K) -
Iwao Kawabe, Tsuyoshi Maki, Ryuichi Sugisaki1981 Volume 15 Issue 4 Pages 183-191
Published: August 20, 1981
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSSubsurface gases have been surveyed in the fault zones around the Median Tectonic Line in western Shikoku Island. Thirty-two bubble gas samples have been collected for this purpose, and their chemical compositions have been determined gas chromatographically. The He/Ar, Ne/Ar, N2/Ar and CH4/Ar ratios of the bubble gas samples suggest that substantial separation of He from Ne has been revealed to interfere seriously with the He/Ar determination using carrier gas of oxygen when the He/Ne ratio of sample gas is as low as in the atmospheric air. Some experimental conditions to reduce the interference have been proposed. The He/Ar, Ne/Ar, N2/Ar and CH4/Ar ratios of the bubble gas samples suggest that substantial amounts of He and CH4 produced in subsurface rocks are added to groundwaters and that almost all Ne, Ar and N2 of subsurface gases are of the atmospheric origin. Concentrations of major and minor gas components of the bubble gases are considerably variable reflecting the types of subsurface rocks. CO2-rich bubble gases with relatively high CH4/Ar ratios are commonly observed in the Sambagawa schist zone, and their He/Ar and CH4/Ar ratios are highly fluctuating according to unsteady discharges of CO2-rich gases containing He and CH4 from underground. N2-rich bubble gases with relatively low CH4/Ar ratios are predominant in the Ryoke granite zone. Some of their He/Ar ratios are fifty to ninety times as high as the atmospheric ratio. The intimate relationship between the bubble gas compositions and the types of subsurface rocks may encourage seismo-geochemical studies of subsurface gases and may suggest that CH4/Ar as well as He/Ar is a possible seismo-geochemical parameter in this region.View full abstractDownload PDF (2754K) -
Yoshimichi Kajiwara, Akira Sasaki, Osamu Matsubara1981 Volume 15 Issue 4 Pages 193-197
Published: August 20, 1981
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSA remarkable isotopic effect of sulfur has been confirmed in the thermal decomposition of pyrite at 600°C in vacuo. The reaction concerned may be written as pyrite(FeS2) → pyrrhotite(FeS) + elemental sulfur(S). 34S/32S ratio of an early fraction of the released elemental sulfur is some 12‰ lower than that of the source pyrite sulfur. Toward the end of the reaction the pyrrhotite dominant solid residue has the isotopic ratio up to about 4.5 ‰ higher than the initial material. A “Rayleigh model” which involves two isotopic fractionation factors, α1(FeS/FeS2) and α2(S/FeS2), seems to hold in the case. The estimated α1 and α2 are 0.9951 and 0.9883, respectively. The result may have significant bearing on sulfur isotope geochemistry, particularly because of the very large isotopic effect at a high temperature.View full abstractDownload PDF (1344K) -
Shigeru Ohde, Yasushi Kitano1981 Volume 15 Issue 4 Pages 199-207
Published: August 20, 1981
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThis report describes protodolomites found in Daito-jima to the east of the Okinawa Islands, Japan. To investigate the conditions for sedimentary protodolomite formation, the distribution and chemical composition of protodolomites were studied through field observations and laboratory analyses. From the thin section studies of carbonate rocks, it was observed that porous parts of coral were cemented by protodolomite crystals and that aragonite in hard tissue of coral was transformed into protodolomite. These observed facts may show that protodolomite was formed through the transformation from aragonite and magnesian calcite in magnesium rich solution. The distribution and chemical composition of protodolomite in Minami-daito-jima suggest that protodolomites may be formed in concentrated seawater.View full abstractDownload PDF (2305K) -
E. G. Imeokparia1981 Volume 15 Issue 4 Pages 209-219
Published: August 20, 1981
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe Afu Younger Granite Complex is the southernmost of the Nigerian Younger Granite Complexes and is composed mainly of biotite granites. They are granites enriched in volatile elements, Li, Rb, F and ore elements such as Sn, W, Zn and Nb. Tin-tungsten - niobium mineralization is associated with the younger phases of the biotite granites. Alkali elements variation particularly Ba/Rb and Rb/Sr ratios indicate the degree of fractionation of the successive phases of the biotite granites, postmagmatic alteration and mineralization in the complex. The granites associated with mineralization generally have higher Rb/Sr and lower Ba/Rb ratios as a result of intensive fractionation and increasing hydrothermal volatile activities. Hydrothermal alteration and mineralization result in even higher Rb/Sr ratios and lower Ba/Rb ratios. It is concluded that the use of Ba/Rb and Rb/Sr ratios offers a more consistent guide to the ore bearing potential of granitic rocks in the Younger granite region, than the use of absolute concentrations of Sn, W and Nb.View full abstractDownload PDF (3038K) -
Naoki Onuma, Shuji Ninomiya, Hiroshi Nagasawa1981 Volume 15 Issue 4 Pages 221-228
Published: August 20, 1981
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSFour new partition coefficient versus ionic radius diagrams have been presented for nepheline-, melilite-, perovskite-, and clinopyroxene-groundmass of a melilite-nepheline basalt, Nyiragongo volcano, Zaire, Africa. The results were discussed on the basis of the “crystal structure control” mechanism.View full abstractDownload PDF (2001K) -
1981 Volume 15 Issue 4 Pages e1
Published: 1981
Released on J-STAGE: February 06, 2009
JOURNAL FREE ACCESSDownload PDF (374K)
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